1. Field of the Invention
The present invention relates to manufacturing metal ferrules for optical fibers used principally for optical telecommunications and the like, and especially relates to a manufacturing method and device for metal ferrules used as connector elements for optical fibers (hereinafter referred to as “metal ferrules”) in which a metal ferrule is obtained from a tube-shaped electroformed layer that is grown by electroforming.
2. Description of the Related Art
A variety of cylindrical ferrules (ferrule: A cylindrical part for coaxially opposing the terminals of optical fiber strings to each other. It is used to connect the opposite ends of optical fiber strings.) are conventionally used as connector elements for connecting optical fibers developed principally for optical telecommunications.
Such a ferrule is conventionally manufactured in the following way: a mixture of zirconia powder and resin is formed by injection molding or extrusion molding into a cylindrical shape and is later baked around 500° C. for decomposing and removing the resin and in addition the same is baked around 1200° C. Thereafter, diamond abrasion is applied to a hole of the aforementioned ferrule (baked product) so as to adjust the hole diameter within the allowable margin of error, and mechanical processing such as grinding is applied to the center of the hole so as to make the periphery of the aforementioned ferrule a true circle.
However, the conventional methods of manufacturing ferrules have difficulties, as follows:    (1) An expensive molding device or metallic pattern is needed for injection molding or extrusion molding and, in addition, such metallic patterns are easily abraded by the zirconia powder, and therefore special processing such as applying cemented carbide to the molding surface of the metallic pattern is necessary, and the abrasion must constantly be monitored so that repairing or changing of the metallic pattern can be performed when necessary.    (2) Time and special skills are needed to perform the diamond abrasion of the piercing hole, and therefore it is difficult to increase productivity.    (3) The baking temperature is high, which requires a great deal of energy at high cost.    (4) According to the type of physical-contact connection (hereinafter referred in short to as a “PC connection”), the ferrule of which material is ceramics, the PC connection must be processed on its end face to form a convex spherical surface, an inclined convex spherical surface, a flat surface, an inclined flat surface, or the like, but the material (ceramics) that is used makes such processing difficult.
To solve these problems, for example, the electroforming method shown in PCT/JP99/No. 06570 (Title of the Invention “Optical fiber connector and ferrule used therein and manufacturing method for the ferrule”) is used to form a ferrule that is made of a metallic material. Such process as included herein is one in which the metal is accumulated around a core string member (the external diameter thereof is the same as the internal diameter of the ferrule) that is dipped in an electroforming cistern to form a tube-shaped electroformed layer, one in which the core string member is removed from the tube-shaped electroformed layer, and one in which the formed electroformed layer is cut into a prescribed length so as to obtain the necessary ferrule.
However, in this electroforming method, the length of the tube-shaped electroformed layer (namely, a part of the core string member that is dipped in the electroforming liquid) is restricted by the depth of the electroforming cistern, and therefore the volume obtained by one electroforming process is small. Also, this is batch-type electroforming processing wherein a number of core string members are repetitively dipped and taken out, and therefore the method is not suitable for mass-production. Also, in order to improve the concentricity, circularity, and cylindricity of the electroformed layer, it is necessary to maintain a fixed distance between the core string member as a cathode and an anode under electroforming, and therefore a contrivance for an electroforming cistern, and placement of electrodes or structure. Furthermore, it is difficult to make the circularity, cylindricity or surface roughness of the tube-shaped electroformed layer within the required accuracy limits.
The Purpose of the Invention
The present invention is based on the aforementioned situation and the purpose of the present invention is to provide a manufacturing method and device by which metal ferrules are continuously manufactured by an electroforming method in such a way as to increase the mass-production of such metal ferrules and to decrease the cost of manufacturing them, as well as to ensure the uniformity of the concentricity, circularity, cylindricity, and electroforming accumulation of the internal/external diameters of the electroformed layer.
A second purpose of the present invention is to provide metal ferrules to be used in practice in the forming process of the tube-shaped electroformed layer.
A third purpose of the present invention is to provide metal ferrules in such a way as to prevent the arising of small hollows in the tube-shaped electroformed layer, especially in the internal wall, and to minimize the depletion of optical signals by removing bubbles in the electroforming liquid in the early stage of electroforming and improving the wetness of the surface of the core string member.
A fourth purpose of the present invention is to provide a manufacturing device for metal ferrules that enables the confirmation of the difference of the electroforming liquid pressure in the vertical direction, convenience for change and maintenance of anodes, and the growth of the electroformed layer, in the electroforming process, by adopting a plurality of electroforming cisterns used in steps as a multitiered structure.